The present invention relates to a process and an apparatus for producing polycarbonate, which is suitable for producing polycarbonate from diphenyl carbonate and an alcohol such as bisphenol A, etc. as raw materials by transesterification upon mixing with a reaction catalyst and additives such as a color adjustment, etc.
In a process using vertical agitation reactors as disclosed in xe2x80x9cPolycarbonate Resinxe2x80x9d, page 66, published by Nikkan Kogyo Shinbun, a larger number of agitation reactors are required for continuous production with increasing scale of the facility, rendering the process uneconomical.
From the viewpoint of a model for perfect mixing vessels ganged together in series as an economical apparatus structure, it is effective to use horizontal agitation reactors capable of providing a large number of such perfect mixing vessels.
A spectacle rim-formed polymerization apparatus as disclosed in FIG. 2.49(b), Cl-43, Cxe2x80xa2Engineering section, of Mechanical Engineering Handbook, is a continuous agitation reactor, which can provide ideal extrusion flow characteristics, that is, a large number of perfect mixing vessels as ganged together in series, but the highly viscous liquid, when treated therein, tends to attach to the surface of the agitator center shaft and reside thereon with increasing liquid viscosity. That is, no sharp residence time distribution function curve can be obtained. Its mode is shown by a delta response curve in FIG. 8, which is based on test data on relations between the number of model vessels for perfect mixing vessels as ganged together in series and the residence time distribution function. In the spectacle rim-formed polymerization apparatus, deviation from the theoretical curve occurs around the point where the dimensionless number of time, t/to, exceeds 1.3. This means that a portion of the liquid resides in the dead zone of agitation, resulting in a problem of polymer quality deterioration.
In FIG. 8, xe2x80x9cnxe2x80x9d is the number of theoretical plates corresponding to perfected mixing vessels. The actual number of Brade partition plates is four stages. And the viscosity is 5 kPaxc2x7s.
An object of the present invention is to provide a process and an apparatus for producing polycarbonate, which can improve the quality of polycarbonate as a polymerization product polymer.
Another object of the present invention is to provide a process and an apparatus for producing polycarbonate, designed to reduce the investment and operating costs.
According to one aspect of the present invention, a process for producing polycarbonate is provided, which comprises subjecting diphenyl polycarbonate and an alcohol such as bisphenol A, etc. as raw materials to polycondensation reaction at elevated temperatures ranging from 200xc2x0 C. to 300xc2x0 C. in vacuum less than or equal to the atmospheric pressure in one or more horizontal cylindrical agitation reactors, as ganged together in series, without any agitator center shaft, with increasing liquid viscosity from 1 Paxc2x7s to 5,000 Paxc2x7s, thereby continuously producing polycarbonate.